Hepatocellular carcinoma (HCC) is the most rapidly increasing type of cancer with high mortality in the United States. Tumor suppressor p53 plays a crucial role in tumor prevention, including HCC, through its regulation of cell cycle arrest, apoptosis and senescence. Recent studies suggested a novel function for p53 in tumor suppression, i.e. p53 regulates energy metabolism. As a hallmark of tumor cells, metabolic changes (e.g. Warburg effect) were recently suggested to be a key contributor to tumorigenesis and a potential target for tumor therapy. We identified a novel p53 target gene, the mitochondrial glutaminase 2 (GLS2), a gene encoding an enzyme involved in mitochondrial respiration, which provides a direct link for p53 and metabolism. Strikingly, our data from a limited number of samples show that GLS2 expression is absent or significantly decreased (by over 20-fold) in almost all of the HCC specimens we analyzed as compared with the adjacent normal or cirrhotic liver tissues. Our preliminary data further suggest that GLS2 may suppress tumorigenesis and regulates energy metabolism. Based on our results, we hypothesize that GLS2 may play a critical role in tumor suppression through its regulation of metabolism. In this proposed study we plan to: 1) determine the GLS2 expression in additional 100 HCC specimens to establish the loss of GLS2 as a common and specific event for HCC which could be a potential tumor biomarker. 2) Test the hypothesis that loss of GLS2 epxression promotes tumorigenesis while restoration of GLS2 expression inhibits liver tumorigenesis in nude mice. 3) Identify mechanisms for GLS2 in tumor suppression. In particular, we will determine GLS2's role in regulation of energy metabolism, stress responses and antioxidantion. 4) Identify mechanisms underlying the loss of the GLS2 expression in HCC. In response to RFA (PA-08-243) entitled Etiology, Prevention, and Treatment of Hepatocellular Carcinoma, this proposed study will greatly increase our understanding of the mechanisms for liver tumorigenesis and expand our understanding of mechanisms of p53 in tumor suppression, especially the role of metabolic changes in tumorigenesis and the role of reversing metabolic changes in tumor therapy. It is our anticipation that this study will have direct potential to provide GLS2 as a novel tumor biomarker and therapeutic target for tumor therapy, especially for HCC.